There are a wide variety of institutional and industrial washing machines in the prior art. One such machine maintains a detergent solution in a reservoir for use by a washing machine. During operation, the machine draws upon or washes within the detergent solution in the reservoir until drained or replenished by fresh solution. In order to maintain a desired concentration of detergent in the reservoir, concentrated detergent must be added periodically to the reservoir.
In commercial and industrial applications, cost, safety, and quality considerations often require that the washing system minimize operator involvement in the process of adding or "charging" the detergent concentrate into the reservoir. Operator involvement is often unnecessarily time consuming and costly, and the detergent concentrate is sometimes caustic and unsafe for handling by an operator. Moreover, many washing operations require very precise machine control of detergent concentration in the reservoir--too low and the washing is less than complete; too high and the washing leaves an undesirable and sometimes unsafe residue.
Commercial and industrial washing systems therefore frequently accomplish charging with an automatic or semi-automatic detergent dispensing apparatus having a fairly large capacity for detergent concentrate. By automating the charging process, these dispensers attempt to minimize labor costs, operator errors or injury, inaccuracy or inconsistency of detergent concentration, and inadequate or unsafe cleaning.
One type of detergent dispensing apparatus is the "demand" dispenser. In the demand dispenser, a conductivity cell forms an electrical bridge or comparator to monitor detergent concentration in the solution emitted from or within the washing machine itself. When the conductivity of the solution in the machine goes above or below a predetermined level, the cell signals the dispenser to either cease or commence dispensing detergent solution until the concentration reaches a desired level, at which point the exact opposite "demand" is made by the conductivity cell or comparator.
In the prior art demand systems, the conductivity cell or comparator is often separate from the actual dispenser which the cell or comparator controls. In addition, the prior art demand systems often work in combination with separately mounted rinse pump apparatus to deliver rinse water when activated by a separately mounted controller. They have thus often required the user to acquire, mount, and maintain a variety of components at separated locations.
Another type of prior art dispenser is hydraulically activated. In one such hydraulic system, a by-pass line from the rinse line is hydraulically linked to the detergent dispenser. Each execution of a rinse cycle activates the dispenser to dispense detergent concentrate in predetermined proportion to the volume of rinse water used. The rinse water in the by-pass is diverted back to the wash tank to mix with both fresh rinse water and injected detergent concentrate to maintain the desired detergent concentration.
Such hydraulic systems suffer from the inherent degradation of the wash solution by the rinse water feedback. They also do not provide precise control of detergent concentration in the wash water.
In these prior art detergent dispensers, the detergent concentrate has typically been liquid or solid. Liquid systems and solid systems both have major drawbacks.
In one liquid concentrate system, for example, a canister of liquid concentrate rests under the wash basin or machine, typically on the floor. A detergent supply line extends from the bottle to a venturi valve mounted on a water delivery line over the wash basin or machine reservoir. Water flow in the water delivery line generates a venturi effect in the venturi valve to draw liquid detergent concentrate from the canister into the supply line and then into the water delivery line to mix with the wash water as it is delivered into the wash basin or machine reservoir.
Liquid concentrate is, however, very heavy and bulky compared to solid detergent concentrates. The weight is difficult for the operator to manage, and the large bulk takes up space and requires much greater storage and shipping expense. Since ease of use and storage and shipping costs are often the dominant factors in determining which system to use, solid concentrate systems are much more prevalent in commercial and industrial applications.
One prevalent solid concentrate system utilizes powdered detergent stored in a translucent plastic supply container. The container is provided with a capped top for storage and shipping. A meshed screen, with apertures finer than the grains of detergent powder, spans the top under the cap. When used, the cap is removed, the container is inverted, the meshed screen is centered over a receptacle on the dispenser, and the inverted container is lowered into the receptacle until it rests securely in place within the receptacle.
A spray nozzle is centered in the receptacle below the meshed screen and above an underlying drain. The spray nozzle sprays fresh water upwards through the meshed screen, which atomizes the spray as it continues upward into the powdered detergent supported over the screen. The powdered detergent concentrate directly overlying the screen is dissolved into the solution, which falls back into the underlying drain. The detergent solution is directed from the drain into a conduit for delivery to a wash basin or machine.
In high volume applications of this type and others as well, the shipping container is large and also serves as the supply container, usually remote from washing apparatus. Examples of such applications are shown in U.S. Pat. Nos. 3,545,438 and 4,020,865.
In lower volume applications, the detergent dispenser is frequently located on or adjacent the wash basin or machine, and the container is much smaller for ease of insertion into the dispenser. One example is disclosed in U.S. Pat. No. 4,063,663.
There are other powdered dispensers. See, for example, U.S. Pat. No. 4,426,362. These and the other powder detergent dispensers have solved a variety of problems, but they too suffer from problems.
For instance, due to increased sanitary standards and demands for shorter wash times, recently developed powdered detergents have relatively complex detergent compositions. These complex detergent compositions are more hazardous to the user, less stable, and more difficult to dissolve in a satisfactorily uniform manner. For a detailed discussion of these problems, see the U.S. patent application referenced in U.S. Pat. No. 4,426,362.
Another problem arises when the powdered detergent includes a mixture of components having differing dissolving rates. Powdered detergents dissolve relatively rapidly because of their high specific areas. Powdered detergents with components having differing dissolving rates will thus yield significantly varying solution composition over relatively short periods of time.
Yet another problem arises when components of the detergent are relatively unstable. An example is a detergent requiring an active chlorine source with an organic defoamer. Due to the instability of the chlorine component, the available chlorine can be lost well before going into the intended the solution. The chlorine instability problem is even more acute with high alkalinity powdered detergents. Many defoamers and chlorine components, for example, are even more unstable in the presence of highly alkaline chemicals, like sodium hydroxide.
Powdered detergents often also have the problem of segregation or stratification of the powdered particles during manufacturing, shipping, handling, etc. Segregation can lead to non-uniform dissolving of the components which have settled to different levels or concentrated at different locations in the container.
Powders also often clog the screen as the spray partially dissolves powders immediately above the screen and the weight of the undissolved powder above jams the partially dissolved powder into screen apertures. The screen thus becomes clogged, sometimes partially and sometimes wholly. If only partially, the rate of dissolving becomes less uniform and reduced (slowing the washing process) as the clog blocks access to powder over the clog. If anywhere near wholly blocked, the clog brings the wash process to a halt until the clog is removed by the operator, either by cleaning or replacing the screen or by replacing the entire container of detergent powder. Either result yields significant problems for the wash process.
One attempt to solve at least some of these problems is the solid-block detergent system disclosed in U.S. Pat. No. 4,426,362. In this system, a container, much like the containers for the smaller volume powder applications described above, contains a solid block of detergent concentrate substantially filling the inside of the container. This block detergent container is also placed in an inverted position in a retaining receptacle, and a water nozzle sprays water upwardly into the container against the solid detergent. The water dissolves the detergent into solution, which, like the powder system described above, then falls back into an underlying drain for delivery to a reservoir and use in washing. The main difference of this system from the other well-known prior-art small-volume powder systems described above, is thus the use of a solid, consistent block of detergent concentrate in the place of powders.
This solid block system does not solve all the problems of powders. The solid block system also raises problems of its own. One problem of the solid block system is the inherent non-uniformity of detergent concentration in the solution it generates. Applicant believes this is caused by several physical limitations on the solid block system.
First, the solid block of detergent is positioned vertically over the spray nozzle so that the upwardly directed spray is always subject to the ever-present downward pull of gravity. Over time, the spray dissolves the lowermost portion of the block, so that the remaining detergent is located further away upwardly from the nozzle. Over time, the spray must travel further and further upwardly from the nozzle and against gravity to reach the surface of the remaining portion of the solid block detergent concentrate. Thus, over time, the force or impact of the spray against the solid block becomes weaker and weaker.
Second, the solid block is sloped so that the neck of the container is narrow at the opening adjacent the nozzle and widens as the vertical distance from the spray nozzle increases. The constant amount of spray from the nozzle must impact a larger and larger surface area, with less and less upward velocity, as the detergent block dissolves upwardly from the neck opening further upwardly into the sloped neck.
A detergent solution of inconsistent concentration results. The concentration becomes weaker and weaker as the block detergent dissolves and the spray must travel a greater distance upwards to cover a wider and wider area.
Another problem is waste. The uppermost portion of the solid block is difficult to dissolve with sufficient concentration, and in any event, cannot all be dissolved by upward spray as desired since the uppermost portion may eventually crumble and fall leading to non-uniform dissolving as with powders. The remaining undissolved solid detergent is thus unusable and wasted. The waste often reaches as much as 10% of the detergent concentrate, which the user must, of course, pay for.
A further problem with the solid block system is the bulk, i.e., volume and weight, of the solid block detergent. Although less bulky than powder detergent concentrate, the solid block detergents occupy significant volume and have substantial weight, especially since most solid block detergents consist of about 15-20% moisture.
Of course, bulk is also a concern for powdered and liquid systems as well.
An additional problem with some of these prior art dispenser systems is the ease of using the wrong detergent concentrate in the wrong environment. Many of the prior art containers are physically interchangeable so that, for example, both a caustic detergent and an identically contained pot and pan cleaner will fit on the same dispenser. A person washing pots and pans can thus burn his or her hands or incur other problems if the wrong container is inserted into the dispenser.